Overnight, crowds could be seen rushing into the sit-in area, lobbing rocks and fire bombs from a nearby bridge and charging toward the few hundred protesters. Vehicles were set on fire and fires burned in the middle of the street.

Apparently, clashes began after protesters blocked the road at about 8 p.m. Marc Mino, a protest organizer, told state television that drivers had provoked the fight after refusing to be searched before entering the protest area.

An eyewitness, George Thabet, said he saw “young thugs in plain clothes” atop the nearby 6th of October bridge hurl Molotov cocktails down at protesters at about 8 p.m., injuring scores of people and setting cars ablaze.

After gunshots were fired, police and soldiers set up tanks at the ends of the road and began firing warning shots to scare of the attackers, Thabet said. By 1:30 a.m., security forces had restored order and protesters resumed the sit-in.

Sectarian violence has challenged Egypt's military rulers, who took over after longtime President Hosni Mubarak was forced to step down in February and have attempted to maintain order ahead of September’s presidential election.

Political analyst Ammar Ali Hassan described the latest violence as "a second phase of what started last week in Imbaba."

"The same people who ignited sectarian violence and were aiming to disrupt the country’s stability and start a civil war between Muslims and Copts to destroy any gains of the January 25th revolution are unleashing their thugs against Coptic demonstrators, especially after efforts to calm down tensions over the last week have been relatively successful," he said.

He rejectedthe possibility that the attackers were religious extremists, and said they were more likely allied with Mubarak.

"We still have many people who belonged to Mubarak’s regime and it’s in their best interest to trigger conflicts like these and keep them alive," Hassan said.

Following the latest religious violence, military leaders promised to respond to Coptic Christian protesters’ demands, including reopening nearly 50 churches. But no trial date has been set for those responsible for last week’s violence.

-- Molly Hennessy-Fiske and Amro Hassan in Cairo

Photo: Egyptian riot police stand guard after clashes in front of the state television building in Cairo early Sunday. An angry mob attacked protesters, mainly Coptic Christians, outside the building, resulting in clashes leaving scores of people injured. Credit: Mohamed Omar/EPA.